Comparison of methods for determining the deliquescence points of single crystalline ingredients and blends

Many crystalline food ingredients undergo dissolution at a critical relative humidity known as the deliquescence point (RH0). Blends of crystalline ingredients exhibit deliquescence lowering, resulting in a deliquescence point (RH0mix) lower than the individual ingredient RH0s. To determine the effects of method type and data collection parameters, these deliquescence measurement methods were compared: saturated solution water activity, dynamic vapor sorption profiles (DVS), and dynamic dewpoint sorption profiles (DDI). Water activity measurements were broadly applicable for measuring deliquescence points when 1-4 g sample, 50-125 μL/g water:solid ratio, and 24-48 h equilibration were used. DVS and DDI techniques should be limited to samples containing 1-2 ingredients due to crystal contact point effects on RH0mix measurement. Recommended DVS parameters are: 1% RH step, 0.01% equilibrium criteria, and 3h maximum time. DDI profiles were consistent with 50-150 mL/min vapor flow rates. Ingredient mutarotation, solute interactions in solution, and contact point limitations affect the determination of deliquescence points.